#include <stdio.h>
#include <math.h>
int main()
{
	int a, b, c;
	double s,S;
	printf("input a,b and c");
	scanf_s("%d%d%d", &a, &b, &c);
	s = (a + b + c) / 2 * a;
	S = sqrt(s * (s - a) * (s - b) * (s - c));
	printf("S=%lf\n", S);
	return 0;
}